Today, customers of DC/DC converters have a need to do DCR current sensing on the inductor, making use of its copper resistance by adding a R-C network in parallel to the buck converter inductor to do voltage sensing across the inductor resistance or alternatively using a shunt to do the sensing. A shunt would be a resistor in the mOhm range, either in the output power rail or in the ground return path. This way, allowing measurement of the current delivered to the load. However, those implementations hurt the efficiency and are usually not as accurate as desired. Especially in mass production trimming and tolerances, as this means additional cost. Further, it is expected that in near future, the switching frequencies of the DC/DC converters will increase, which means that the inductance value of the inductor will become smaller, which in turn will result in a significantly lower on-resistance of the inductor. This will cause severe difficulties in reading out the current in the inductor by making use of the small DCR of its copper windings. Again, a shunt resistor may be applied for DCR current sensing, which will however cause an additional power loss. Further, an expensive and precise shunt sense resistor is needed. An opportunity could be to make use of a copper trace that is a part of a printed circuit board as a shunt resistor. However, this will require a very tight production control of the printed circuit boards in order to ensure that the resistance of this printed shunt resistor is well defined and always has the same value. This could be achieved by laser trimming the printed copper trace, but again, this would cause additional costs and would increase production complexity.
Customers designing DC/DC converters are further aiming for a high efficiency, a small form factor and a high integration of components. In principle, this is provided by multi chip modules (MCM). A further goal is to reduce the cost of the DC/DC converter while not sacrificing performance and efficiency.